Guide loop height adjustment for vehicle passenger seat belts

ABSTRACT

A guide loop height adjustment arrangement for a driver&#39;s seat belt has a drive that raises and lowers a guide loop in response to a sensed change in the position of the driver&#39;s mirror. The change in the mirror position is indicative of the presence of a seat occupant with a different shoulder height from the preceding seat occupant and therefore causes the guide loop height to be adjusted.

This invention relates to guide loop height adjustment for vehiclepassenger seat belts.

Vehicle passenger seat belt systems as employed in private motor carsare typically three point systems with lap and diagonal belt webbings.Usually the webbing is drawn from the reel of an emergency lockingretractor via a passenger shoulder height guide loop before passingdiagonally downward across the front of the occupant. The webbing thenpasses via a buckle tongue and returns across the lap of the occupant toa floor anchorage located generally beneath the guide loop.

In the interests of passenger comfort and safety it is now quite commonfor vehicle manufacturers to install guide loops which are manuallyadjustable for height by the occupant so that the point at which thewebbing changes direction is approximately the height of the adjacentshoulder of the respective occupant. In cases where there is no suchadjustment the guide loop is positioned by the manufacturer to ideallysuit a person of notional average shoulder height. Occupants ofnon-average shoulder height may be subject to reduced safety and/orcomfort.

In a case where manual height adjustment is provided by the vehiclemanufacturer, there is obviously a possibility that an occupant may benon-vigilant either through complete unawareness of the presence of theadjustment facility or simply inadvertently forgetting to suitably resetthe adjustment.

The object of the present invention is to provide means for making anautomatic adjustment of the height of a seat belt guide loop in spite ofnon-vigilance by an occupant.

According to the present invention there is provided a guide loop heightadjustment arrangement for a vehicle drivers' seat belt comprising adrive means operable to raise and lower a guide loop having meansoperable to sense a change of position of a drivers' mirror and meansresponsive to such change indicative of the presence of a seat occupantof different shoulder height from a preceding seat occupant to activatesaid drive means to reposition said guide loop.

In one embodiment of the invention computation means is provided whichutilises the positions of adjustable nearside and offside rear viewdriving mirrors and the position of an adjustable drivers' seat tocalculate a drivers' shoulder height and activates said drive means toposition said guide loop.

In an alternative embodiment of the invention means may be provided forsensing a departure of the tilt angle of an interior rear view mirrorfrom a nominal average setting and correspondingly making a departure ofthe height setting of a guide loop based thereupon.

In order that the invention may be more clearly understood and readilycarried into effect the same will be further described by way of anexample with reference to the accompanying drawing which is a schematicillustration of a guide loop height adjustment system.

Referring to the drawing, the height adjuster for the pillar mountedwebbing guide loop 2 of a vehicle drivers' seat belt is denoted byreference 1. Typically, this is located within the `B` post adjacent thedrivers' seat and the height of the guide loop 2 is adjustable therebyto suit a range of shoulder heights for the seat occupant. The height ofthe guide loop 2 is variable by a reversible d.c drive motor 3mechanically linked thereto by a toothed belt or shaft drive gearmechanism and the position is sensed by a position transducer 4 whichmay comprise an electrical potentiometer providing a position feedbacksignal to a signal comparator 5. A control input to 5 is derived from anelectronic computation and control unit 6.

For the purposes of controlling the motor 3, the unit 6 makes use ofoutput signals derived from the fore and aft seat position, the seatheight where this is adjustable and also the angles of tilt and swing ofleft and right hand driving mirrors.

The left hand and right hand mirrors are shown diagrammatically at 8 and9 both of which are adjustable by the vehicle driver manually or byelectric motor from the driving position. These mirrors are alsoprovided with respective transducer units 10 and 11. Transducer unit 10provides a left-tilt output signal (θ2) on output 12 and a swing output(θ1) on output 13. Transducer unit 11 provides a right hand tilt outputsignal on (γ2) output 14 and a swing output signal (θ1) on output 15.All four transducer outputs are fed to the computation and control unit6 along with transducer outputs on lines 17 and 18 from a fore and afttransducer 19 and a height transducer 20 respectively of a seat positionunit 21.

The seat position unit 21 also provides a seat occupancy signal on anoutput 22 to govern the provision of a seat occupancy signal at an input23 to the computation unit 6. Such seat occupancy signal may beunnecessary where the seat belt is provided with a buckle having meansfor sensing the presence of a locked in buckle tongue. Typically suchmeans are provided in some existing systems to initiate a visible oraudible seat belt warning to an occupant and may therefore also be usedto provide an input such as 23.

In operation, when the computation unit 6 receives a seat occupancysignal on its input 23, this signal acts as an enabling input inresponse to which the computation unit 6 begins to continuously monitorthe inputs on lines 12, 13, 14, 15, 17 and 18. These signals will bechanged dependent upon any new mirror settings made by the driver andbased on internally stored data. The unit 6 performs the necessarycalculation to determine a preferred position for the guide loop. Thecomparator 5 compares the output of unit 6 with the position feedbacksignal derived from transducer 4 and actuates the motor 3 to drive theheight adjuster 1 to a position at which the position represented by theoutput of transducer 4 equals the position represented by the output ofunit 6.

The above outlined system operates upon the basis that the preferreddirection of webbing, from the guide loop to the shoulder of anoccupant, is approximately horizontal and this is normally achievablewith an average driver with the height adjuster 1 set at a mid-position.A driver of somewhat greater height will require the seat lower andfurther aft and broadly speaking these parameters can therefore be usedto set the height adjuster at a somewhat higher location. Howevershoulder height in a seated position is clearly not strictlycorrelatable with leg length and/or head height of an occupant.Nevertheless, by providing transducers which indicate mirror swing andtilt angles, of correctly adjusted mirrors, further information is madeavailable to the computation circuit 6 which is related to eye positionand this enables the computation circuit to provide a more precise andstatistically more correct signal representation of desired guide loopheight.

In some vehicles it may be sufficient to dispense with certain of thetransducer signals. For example, some vehicles may not have seat heightadjustment.

Again, if the driver adjusts only the seat and one mirror, typically thedrivers' side mirror, the computation circuit 6 may be adapted to sensethis and reject the inputs from any non-reset mirror.

Since there is in general a predictable correlation between thetransducer outputs from the respective individual mirrors and thedrivers' seat, in order to deal with the event of a totalincompatibility, the computation circuit may be adapted as a precautionto set the guide loop height for an average driver.

In an alternative and possibly simplified embodiment of the inventionthe drivers' internal rear view mirror may be fitted with a transducerwhich provides an output signal indicative of an elevation (tilt) anglethereof which is comfortable for driver vision in the normal drivingposition with the seat correctly adjusted. The computation circuit maythen be designed to simply correlate a departure of the guide loopheight setting from an average position with any departure of mirrortilt angle from an average position. Whilst such a system introduces theneed for a transducer and any necessary electrical connectionsassociated with the interior rear view mirror, it avoids the need forsuch transducers and at least a near-side mirror drive motor associatedwith the exterior driving mirrors which are always regarded as morevulnerable to accidental damage. Moreover, this alternative does notcall for an albeit unpredictable correlation between seat positionsignals and a desirable guide loop height setting. An additionaladvantage resides in the fact that most drivers may instinctively makesmall adjustments to the interior rear view mirror as of greaterpriority than adjustments to the exterior side mirrors. The probabilitythat the guide loop height is more correctly set is therefore possiblyhigher and the system to achieve it may be somewhat simplified.

We claim:
 1. A guide loop height adjustment arrangement for a vehicledrivers' seat belt comprising a drive means operable to raise and lowera guide loop having means operable to sense a change of position of adrivers' mirror and means responsive to such change indicative of thepresence of a seat occupant of different shoulder height from apreceding seat occupant to activate said drive means to reposition saidguide loop.
 2. A guide loop height adjustment arrangement according toclaim 1, comprising means for sensing the positions of adjustablenearside and offside rear view driving mirrors, means for sensing theposition of an adjustable drivers seat and computation means responsiveto the outputs of said sensing means to calculate a drivers shoulderheight and to activate said drive means to position said guide loop inaccordance with the calculated shoulder height.
 3. A guide loop heightadjustment arrangement according to claim 2, wherein the means forsensing the position of the adjustable' drivers seat senses the fore andaft seat position and the seat height where this is adjustable.
 4. Aguide loop height adjustment arrangement according to claim 2, whereinthe mirror position sensing means detects the angles of tilt and swingof the nearside and offside rear view driving means.
 5. A guide loopheight adjustment arrangement according to claim 2, wherein the outputof any one of the said sensing means is disregarded by the computationmeans if it does not alter with changes in the outputs of the othersensing means.
 6. A guide loop height adjustment arrangement accordingto claim 1 comprising means for sensing a departure of the tilt angle ofan interior rear view mirror from a nominal average setting andcomputation means responsive to changes in output of said sensing meansto calculate a drivers shoulder height and to activate said drive meansto position said guide loop in accordance with the calculated shoulderheight.
 7. A guide loop height adjustment arrangement according to claim1, comprising means for sensing the actual position of the guide loop,and comparator means for comparing the sensed position of the guide loopwith the output of the computation means to provide a difference signalwhich activates the drive means to reposition said loop.
 8. A guide loopheight adjustment arrangement according to claim 3, wherein the mirrorposition sensing means detects the angles of tilt and swing of thenearside and offside rear view driving means.
 9. A guide loop heightadjustment arrangement according to claim 3, wherein the output of anyone of the said sensing means is disregarded by the computation means ifit does not alter with changes in the outputs of the other sensingmeans.
 10. A guide loop height adjustment arrangement according to claim4, wherein the output of any one of the said sensing means isdisregarded by the computation means if it does not alter with changesin the outputs of the other sensing means.